In the conventional process of manufacturing a knitted bag, raw material is firstly knitted into a double-layered material strip which has upper and lower layers and is seamless on both sides. The double-layered material strip is then printed, sealed and cut into pieces, thus forming a knitted bag with two seamless sides.
However, the bottom corners of the knitted bag produced in the above-described way are liable to be broken because they are subjected to the greatest relative heavy loading such that an additional welting operation during the sealing process can not improve their endurance.
To solve the above-mentioned problem, a straightforward method is forming folding on both sides of the material strip and thereafter performing a welting process and the sealing process. In fact, this is the method by which a paper bag's loading ability is enhanced.
However, the knitted bag cannot be folded on both sides as with the paper bag, but requires a further process as follows. As shown in FIG. 4, the double-layer material strip (step A) should be expanded (step B), indented on both sides (step C), and formed into folding (step D). Nevertheless, the commercially available knitted bags have no folding on both sides because the current manufacturing skill is not sufficient to form such folding to increase structural strength.